In this presentation, direct numerical simulation results of gravity waves encountering a mesosphere inversion layer (MIL) from an anelastic model will be reported. The MIL has a moderate static stability enhancement centered around 75 km and a layer of weaker static stability above. Two scenarios of representative gravity wave packets are examined here; specifically, the gravity wave packets have an initial horizontal wavelengths of 20 km and vertical wavelengths of 20km and 40 km, respectively. Both three dimensional and two dimensional (i.e., streamwise and vertical) simulations are performed. The instability dynamics for these MIL cases will be described. Implications for mixing will also be discussed. For instance, we find that instabilities occur within the MIL when the gravity wave amplitude approaches that required for gravity wave breaking due to compression of the vertical wavelength accompanying the increasing static stability. Also, we have found that mixing is much weaker than what had been generally assumed in the past for those cases considered.